The present invention relates to a pin for holding and/or cooling of ceramic coatings in hot reaction chambers, particularly to a pin which is composed of two components.
In hot reaction chambers, such as for example in furnace chambers of coal gasifiers, high temperatures prevail which are required for the course of the desired reactions and/or for a liquid slag withdrawal. As a rule it is necessary here to provide the walls of the hot reaction chambers with a respective temperature-resistant ceramic coating. This coating which normally is formed as a ramming or spraying mass is applied on the walls of the hot reaction chambers and serves for protecting these walls from damage by the action of the high temperature and at the same time for providing the required heat insulation of the hot reaction chamber so as to reliably hold the desired high reaction temperatures inside the chamber. The walls of the hot reaction chambers can be naturally so-called tubular walls, when for example the hot reaction chamber is a melting chamber of a vaporizer or a reaction chamber of a coal pressure gasifier.
For holding and/or cooling the ceramic coating, the walls of the hot reaction chamber are normally provided with pins on which the ceramic coating is mounted. Aproximately two thousand pins are used per square meter of the coating. These pins were produced from non-alloyed steel. However, it has been shown that these pins, in conditions of high temperature acting in the hot reaction chambers, are oxidized and partially thinned by corrosion after relatively short operation times. Because of this, these pins were replaced by pins of high oxidation-resistant steels, for example chromium-aluminum steels. However, this causes another problem. In the event of welding of such pins with the wall of the hot reaction chambers, after a relatively short operation time an embrittling of these pins takes place, which leads to shapeless breakage of the pins at the pin foot. The new pin insertion and new coating of the walls of the hot reaction chambers, which is required after this, leads to considerable operational stoppages and expenditures. It has also been shown that by welding such pins with the wall of the hot reaction chambers, damage to the wall material is caused. This damage is reduced first of all to diffensions process and texture changes, for example decarbonization process, which is responsible for different material composition between the pin and the wall. This damage to the wall material increases naturally with each eventually required new pin introduction. In thin hot reactor chambers loaded in their interior, such as for example the tubular walls of coal pressure gasifiers, this can lead to a considerable reduction of the service life.
To eliminate these problems, it is known to make a compromise in the material selection. Based on this approach, pins are produced with relatively low alloy chromium steel which have a better corrosion and oxidation resistance as compared with the pins of non-alloyed steel, and also is not so heavily inclined to embrittling. Such a compromise is, however, unsatisfactory in many cases, particularly when in hot reaction chambers relatively high temperatures take place. It is also known to make a pin of two components, including a non-alloyed steel core and a sleeve of an oxidation-resistant material. The welding end of this pin is conical, so that the welding connection is first of all produced by the non-alloyed core material. The pin cap facing towards the hot reaction chamber is, however, not subjected to the reaction conditions in the hot reaction chamber without protection, so that at least the non-alloyed steel core of this pin is subjected to respective damages.
Finally, experiments have been conducted to use a pin which has a pin lower part of a non-alloyed steel and a pin upper part of an oxidation-resistant material arranged on the pin lower part and welded by straight welding seams. This pin does not, however, prove to be acceptable in practice, since as expected in the condition of high temperature a breakage in the welding connection between the pin upper part and the pin lower part occurs.
Since for the operability and effectiveness of a hot reaction chamber, the mounting of the ceramic coating which depends on the service life of the pins is of decisive importance, the solution of the above described problems has great practical importance.